Thermoplastic elastomers of the type known as polyetherimide esters provide a variety of unique and excellent properties and are particularly useful in extrusion and molding applications.
Polyetherimide esters prepared from diols, dicarboxylic acids and polyoxyalkylene diimide diacids are thermoplastic elastomers having an excellent combination of stress-strain properties, low tensile set, high melting temperatures and excellent strength, toughness and flexibility properties. All of these properties are variously useful in many elastomer applications. Polyetherimide esters also process well, due to their rapid crystallization rate and excellent moldability characteristics. Elastomers with the low flexural modulus of polyetherimide esters in combination with any of the aforementioned advantageous properties have gained wide acceptance in the field of thermoplastic elastomers.
Nonetheless it has now been found that polyetherimide esters can be improved or enhanced for certain applications, especially with respect to improving the "softness" (i.e., lower durometer) of the elastomer, while retaining satisfactory tensile properties.
The improvements are accomplished by the incorporation of effective amounts of certain rubber modifiers of the type known as multistage interpolymers. It is further surprising, however, that elastomeric blends incorporating the selected rubber modifiers can be processed to avoid the delamination or phase separation (or so-called "cheesiness") expected for the combination of thermoplastic elastomers and typical rubber products.
In particular it has been found that copolyetherimide ester elastomers can be improved by incorporation of effective amounts of rubber modifiers characterized as a multi-stage, or sequentially produced interpolymer product, specifically a thermoplastic elastomer comprised of a crosslinked polyacrylate rubbery phase which is interpenetrated by a crosslinked styrenic phase. This multistage interpolymer elastomer has been extruded to provide a rubber product, and has been added to thermoplastic resins as an impact strength improving additive. See, for example, U.S. Pat. application Ser. No. 064,892, filed Jun. 19, 1987 and which is incorporated by reference.
It has now been surprisingly found that effective amounts of the aforementioned multistage polymer modifier can be combined with a rubbery polyetherimide ester elastomer product and which will thereby exhibit improved modulus and tensile properties as mentioned above.